condition_variable

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// <condition_variable> -*- C++ -*-

// Copyright (C) 2008-2026 Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library.  This library is free
// software; you can redistribute it and/or modify it under the
// terms of the GNU General Public License as published by the
// Free Software Foundation; either version 3, or (at your option)
// any later version.

// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// Under Section 7 of GPL version 3, you are granted additional
// permissions described in the GCC Runtime Library Exception, version
// 3.1, as published by the Free Software Foundation.

// You should have received a copy of the GNU General Public License and
// a copy of the GCC Runtime Library Exception along with this program;
// see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
// <http://www.gnu.org/licenses/>.

/** @file include/condition_variable
 *  This is a Standard C++ Library header.
 */

#ifndef _GLIBCXX_CONDITION_VARIABLE
#define _GLIBCXX_CONDITION_VARIABLE 1

#ifdef _GLIBCXX_SYSHDR
#pragma GCC system_header
#endif

#include <bits/requires_hosted.h> // threading primitive

#if __cplusplus < 201103L
# include <bits/c++0x_warning.h>
#else

#include <bits/chrono.h>
#include <bits/error_constants.h>
#include <bits/std_mutex.h>
#include <bits/unique_lock.h>
#include <bits/alloc_traits.h>
#include <bits/shared_ptr.h>
#include <bits/cxxabi_forced.h>

#if __cplusplus > 201703L
# include <stop_token>
#endif

#if defined(_GLIBCXX_HAS_GTHREADS)

namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION

  /**
   * @defgroup condition_variables Condition Variables
   * @ingroup concurrency
   *
   * Classes for condition_variable support.
   * @{
   */

  /// cv_status
  enum class cv_status { no_timeout, timeout };

  /// condition_variable
  class condition_variable
  {
    using steady_clock = chrono::steady_clock;
    using system_clock = chrono::system_clock;
#ifdef _GLIBCXX_USE_PTHREAD_COND_CLOCKWAIT
    using __clock_t = steady_clock;
#else
    using __clock_t = system_clock;
#endif

    __condvar _M_cond;

  public:
    typedef __gthread_cond_t*           native_handle_type;

    condition_variable() noexcept;
    ~condition_variable() noexcept;

    condition_variable(const condition_variable&) = delete;
    condition_variable& operator=(const condition_variable&) = delete;

    void
    notify_one() noexcept;

    void
    notify_all() noexcept;

    void
    wait(unique_lock<mutex>& __lock);

    template<typename _Predicate>
      void
      wait(unique_lock<mutex>& __lock, _Predicate __p)
      {
        while (!__p())
          wait(__lock);
      }

#ifdef _GLIBCXX_USE_PTHREAD_COND_CLOCKWAIT
    template<typename _Duration>
      cv_status
      wait_until(unique_lock<mutex>& __lock,
                 const chrono::time_point<steady_clock, _Duration>& __atime)
      { return __wait_until_impl(__lock, __atime); }
#endif

    template<typename _Duration>
      cv_status
      wait_until(unique_lock<mutex>& __lock,
                 const chrono::time_point<system_clock, _Duration>& __atime)
      { return __wait_until_impl(__lock, __atime); }

    template<typename _Clock, typename _Duration>
      cv_status
      wait_until(unique_lock<mutex>& __lock,
                 const chrono::time_point<_Clock, _Duration>& __atime)
      {
#if __cplusplus > 201703L
        static_assert(chrono::is_clock_v<_Clock>);
#endif
        using __s_dur = typename __clock_t::duration;
        const typename _Clock::time_point __c_entry = _Clock::now();
        const __clock_t::time_point __s_entry = __clock_t::now();
        const auto __delta = __atime - __c_entry;
        const auto __s_atime = __s_entry +
          chrono::__detail::ceil<__s_dur>(__delta);

        if (__wait_until_impl(__lock, __s_atime) == cv_status::no_timeout)
          return cv_status::no_timeout;
        // We got a timeout when measured against __clock_t but
        // we need to check against the caller-supplied clock
        // to tell whether we should return a timeout.
        if (_Clock::now() < __atime)
          return cv_status::no_timeout;
        return cv_status::timeout;
      }

    template<typename _Clock, typename _Duration, typename _Predicate>
      bool
      wait_until(unique_lock<mutex>& __lock,
                 const chrono::time_point<_Clock, _Duration>& __atime,
                 _Predicate __p)
      {
        while (!__p())
          if (wait_until(__lock, __atime) == cv_status::timeout)
            return __p();
        return true;
      }

    template<typename _Rep, typename _Period>
      cv_status
      wait_for(unique_lock<mutex>& __lock,
               const chrono::duration<_Rep, _Period>& __rtime)
      {
        using __dur = typename steady_clock::duration;
        return wait_until(__lock,
                          steady_clock::now() +
                          chrono::__detail::ceil<__dur>(__rtime));
      }

    template<typename _Rep, typename _Period, typename _Predicate>
      bool
      wait_for(unique_lock<mutex>& __lock,
               const chrono::duration<_Rep, _Period>& __rtime,
               _Predicate __p)
      {
        using __dur = typename steady_clock::duration;
        return wait_until(__lock,
                          steady_clock::now() +
                          chrono::__detail::ceil<__dur>(__rtime),
                          std::move(__p));
      }

    native_handle_type
    native_handle()
    { return _M_cond.native_handle(); }

  private:
#ifdef _GLIBCXX_USE_PTHREAD_COND_CLOCKWAIT
    template<typename _Dur>
      cv_status
      __wait_until_impl(unique_lock<mutex>& __lock,
                        const chrono::time_point<steady_clock, _Dur>& __atime)
      {
        __gthread_time_t __ts = chrono::__to_timeout_gthread_time_t(__atime);
        _M_cond.wait_until(*__lock.mutex(), CLOCK_MONOTONIC, __ts);

        return (steady_clock::now() < __atime
                ? cv_status::no_timeout : cv_status::timeout);
      }
#endif

    template<typename _Dur>
      cv_status
      __wait_until_impl(unique_lock<mutex>& __lock,
                        const chrono::time_point<system_clock, _Dur>& __atime)
      {
        __gthread_time_t __ts = chrono::__to_timeout_gthread_time_t(__atime);
        _M_cond.wait_until(*__lock.mutex(), __ts);

        return (system_clock::now() < __atime
                ? cv_status::no_timeout : cv_status::timeout);
      }
  };

  void
  notify_all_at_thread_exit(condition_variable&, unique_lock<mutex>);

  struct __at_thread_exit_elt
  {
    __at_thread_exit_elt* _M_next;
    void (*_M_cb)(void*);
  };

_GLIBCXX_BEGIN_INLINE_ABI_NAMESPACE(_V2)

  /// condition_variable_any
  // Like above, but mutex is not required to have try_lock.
  class condition_variable_any
  {
#ifdef _GLIBCXX_USE_PTHREAD_COND_CLOCKWAIT
    using __clock_t = chrono::steady_clock;
#else
    using __clock_t = chrono::system_clock;
#endif
    condition_variable                  _M_cond;
    shared_ptr<mutex>                   _M_mutex;

    // scoped unlock - unlocks in ctor, re-locks in dtor
    template<typename _Lock>
      struct _Unlock
      {
        explicit _Unlock(_Lock& __lk) : _M_lock(__lk) { __lk.unlock(); }

#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
        ~_Unlock() noexcept(false)
        {
          if (uncaught_exception())
            {
              __try
              { _M_lock.lock(); }
              __catch(const __cxxabiv1::__forced_unwind&)
              { __throw_exception_again; }
              __catch(...)
              { }
            }
          else
            _M_lock.lock();
        }
#pragma GCC diagnostic pop

        _Unlock(const _Unlock&) = delete;
        _Unlock& operator=(const _Unlock&) = delete;

        _Lock& _M_lock;
      };

  public:
    condition_variable_any() : _M_mutex(std::make_shared<mutex>()) { }
    ~condition_variable_any() = default;

    condition_variable_any(const condition_variable_any&) = delete;
    condition_variable_any& operator=(const condition_variable_any&) = delete;

    void
    notify_one() noexcept
    {
      lock_guard<mutex> __lock(*_M_mutex);
      _M_cond.notify_one();
    }

    void
    notify_all() noexcept
    {
      lock_guard<mutex> __lock(*_M_mutex);
      _M_cond.notify_all();
    }

    template<typename _Lock>
      void
      wait(_Lock& __lock)
      {
        shared_ptr<mutex> __mutex = _M_mutex;
        unique_lock<mutex> __my_lock(*__mutex);
        _Unlock<_Lock> __unlock(__lock);
        // *__mutex must be unlocked before re-locking __lock so move
        // ownership of *__mutex lock to an object with shorter lifetime.
        unique_lock<mutex> __my_lock2(std::move(__my_lock));
        _M_cond.wait(__my_lock2);
      }


    template<typename _Lock, typename _Predicate>
      void
      wait(_Lock& __lock, _Predicate __p)
      {
        while (!__p())
          wait(__lock);
      }

    template<typename _Lock, typename _Clock, typename _Duration>
      cv_status
      wait_until(_Lock& __lock,
                 const chrono::time_point<_Clock, _Duration>& __atime)
      {
        shared_ptr<mutex> __mutex = _M_mutex;
        unique_lock<mutex> __my_lock(*__mutex);
        _Unlock<_Lock> __unlock(__lock);
        // *__mutex must be unlocked before re-locking __lock so move
        // ownership of *__mutex lock to an object with shorter lifetime.
        unique_lock<mutex> __my_lock2(std::move(__my_lock));
        return _M_cond.wait_until(__my_lock2, __atime);
      }

    template<typename _Lock, typename _Clock,
             typename _Duration, typename _Predicate>
      bool
      wait_until(_Lock& __lock,
                 const chrono::time_point<_Clock, _Duration>& __atime,
                 _Predicate __p)
      {
        while (!__p())
          if (wait_until(__lock, __atime) == cv_status::timeout)
            return __p();
        return true;
      }

    template<typename _Lock, typename _Rep, typename _Period>
      cv_status
      wait_for(_Lock& __lock, const chrono::duration<_Rep, _Period>& __rtime)
      { return wait_until(__lock, __clock_t::now() + __rtime); }

    template<typename _Lock, typename _Rep,
             typename _Period, typename _Predicate>
      bool
      wait_for(_Lock& __lock,
               const chrono::duration<_Rep, _Period>& __rtime, _Predicate __p)
      { return wait_until(__lock, __clock_t::now() + __rtime, std::move(__p)); }

#ifdef __glibcxx_jthread
    template <class _Lock, class _Predicate>
    bool wait(_Lock& __lock,
              stop_token __stoken,
              _Predicate __p)
    {
      if (__stoken.stop_requested())
        {
          return __p();
        }

      std::stop_callback __cb(__stoken, [this] { notify_all(); });
      shared_ptr<mutex> __mutex = _M_mutex;
      while (!__p())
        {
          unique_lock<mutex> __my_lock(*__mutex);
          if (__stoken.stop_requested())
            {
              return false;
            }
          // *__mutex must be unlocked before re-locking __lock so move
          // ownership of *__mutex lock to an object with shorter lifetime.
          _Unlock<_Lock> __unlock(__lock);
          unique_lock<mutex> __my_lock2(std::move(__my_lock));
          _M_cond.wait(__my_lock2);
        }
      return true;
    }

    template <class _Lock, class _Clock, class _Duration, class _Predicate>
    bool wait_until(_Lock& __lock,
                    stop_token __stoken,
                    const chrono::time_point<_Clock, _Duration>& __abs_time,
                    _Predicate __p)
    {
      if (__stoken.stop_requested())
        {
          return __p();
        }

      std::stop_callback __cb(__stoken, [this] { notify_all(); });
      shared_ptr<mutex> __mutex = _M_mutex;
      while (!__p())
        {
          bool __stop;
          {
            unique_lock<mutex> __my_lock(*__mutex);
            if (__stoken.stop_requested())
              {
                return false;
              }
            _Unlock<_Lock> __u(__lock);
            unique_lock<mutex> __my_lock2(std::move(__my_lock));
            const auto __status = _M_cond.wait_until(__my_lock2, __abs_time);
            __stop = (__status == std::cv_status::timeout) || __stoken.stop_requested();
          }
          if (__stop)
            {
              return __p();
            }
        }
      return true;
    }

    template <class _Lock, class _Rep, class _Period, class _Predicate>
    bool wait_for(_Lock& __lock,
                  stop_token __stoken,
                  const chrono::duration<_Rep, _Period>& __rel_time,
                  _Predicate __p)
    {
      auto __abst = std::chrono::steady_clock::now() + __rel_time;
      return wait_until(__lock,
                        std::move(__stoken),
                        __abst,
                        std::move(__p));
    }
#endif
  };

_GLIBCXX_END_INLINE_ABI_NAMESPACE(_V2)

  /// @} group condition_variables
_GLIBCXX_END_NAMESPACE_VERSION
} // namespace

#endif // _GLIBCXX_HAS_GTHREADS
#endif // C++11
#endif // _GLIBCXX_CONDITION_VARIABLE